1. Field of the Invention
This invention relates to liquid-cooled nuclear reactors and more particularly to reactors having linearly movable control rods and guide tubes for guiding the control rods through the reactor vessel upper internals and into aligned core fuel assemblies.
2. Description of the Prior Art
Many liquid-cooled nuclear reactors utilize a core of vertically positioned fuel assemblies within a reactor vessel. A reactor upper internals structure is positioned above the fuel assemblies and, among other functions, serves to restrain upward movement of the fuel assemblies and to guide reactor control rods from above the fuel assemblies into and out of the core.
The large volume and velocity of reactor coolant exiting the core, in the range of hundreds of thousands of gallons per minute, results in significant loads on the reactor upper internals components and the control rods. Also, the control rod guide tubes of the upper internals impose a frictional restraint upon the control rods during motion which detrimentally affects the insertion time interval. It is therefore desirable to provide structure which accounts for these loads and mitigates their potentially detrimental effects.